NAND cell encoding to improve data integrity

ABSTRACT

Devices and techniques for NAND cell encoding to improve data integrity are disclosed herein. A high-temperature indicator is obtained and a write operation is received. The write operation is then performed on a NAND cell using a modified encoding in response to the high-temperature indicator. The modified encoding includes a reduced number of voltage distribution positions from an unmodified encoding without changing voltage distribution widths, where each voltage distribution corresponds to a discrete set of states an encoding.

PRIORITY APPLICATION

This application is a continuation of U.S. application Ser. No. 15/692,508, filed Aug. 31, 2017, which is incorporated herein by reference in its entirety.

BACKGROUND

Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic devices. There are many different types of memory, including volatile and non-volatile memory.

Volatile memory requires power to maintain its data, and includes random-access memory (RAM), dynamic random-access memory (DRAM), or synchronous dynamic random-access memory (SDRAM), among others.

Non-volatile memory can retain stored data when not powered, and includes flash memory, read-only memory (ROM), electrically erasable programmable ROM (EEPROM), static RAM (SRAM), erasable programmable ROM (EPROM), resistance variable memory, such as phase-change random-access memory (PCRAM), resistive random-access memory (RRAM), magnetoresistive random-access memory (MRAM), or 3D XPoint™ memory, among others.

Flash memory is utilized as non-volatile memory for a wide range of electronic applications. Flash memory devices typically include one or more groups of one-transistor, floating gate or charge trap memory cells that allow for high memory densities, high reliability, and low power consumption.

Two common types of flash memory array architectures include NAND and NOR architectures, named after the logic form in which the basic memory cell configuration of each is arranged. The memory cells of the memory array are typically arranged in a matrix. In an example, the gates of each floating gate memory cell in a row of the array are coupled to an access line (e.g., a word line). In a NOR architecture, the drains of each memory cell in a column of the array are coupled to a data line (e.g., a bit line). In a NAND architecture, the drains of each memory cell in a string of the array are coupled together in series, source to drain, between a source line and a bit line.

Both NOR and NAND architecture semiconductor memory arrays are accessed through decoders that activate specific memory cells by selecting the word line coupled to their gates. In a NOR architecture semiconductor memory array, once activated, the selected memory cells place their data values on bit lines, causing different currents to flow depending on the state at which a particular cell is programmed. In a NAND architecture semiconductor memory array, a high bias voltage is applied to a drain-side select gate (SGD) line. Word lines coupled to the gates of the unselected memory cells of each group are driven at a specified pass voltage (e.g., Vpass) to operate the unselected memory cells of each group as pass transistors (e.g., to pass current in a manner that is unrestricted by their stored data values). Current then flows from the source line to the bit line through each series coupled group, restricted only by the selected memory cells of each group, placing current encoded data values of selected memory cells on the bit lines.

Each flash memory cell in a NOR or NAND architecture semiconductor memory array can be programmed individually or collectively to one or a number of programmed states. For example, a single-level cell (SLC) can represent one of two programmed states (e.g., 1 or 0), representing one bit of data.

However, flash memory cells can also represent one of more than two programmed states, allowing the manufacture of higher density memories without increasing the number of memory cells, as each cell can represent more than one binary digit (e.g., more than one bit). Such cells can be referred to as multi-state memory cells, multi-digit cells, or multi-level cells (MLCs). In certain examples, MLC can refer to a memory cell that can store two bits of data per cell (e.g., one of four programmed states), a triple-level cell (TLC) can refer to a memory cell that can store three bits of data per cell (e.g., one of eight programmed states), and a quad-level cell (QLC) can store four bits of data per cell. MLC is used herein in its broader context, to can refer to any memory cell that can store more than one bit of data per cell (i.e., that can represent more than two programmed states).

Traditional memory arrays are two-dimensional (2D) structures arranged on a surface of a semiconductor substrate. To increase memory capacity for a given area, and to decrease cost, the size of the individual memory cells has decreased. However, there is a technological limit to the reduction in size of the individual memory cells, and thus, to the memory density of 2D memory arrays. In response, three-dimensional (3D) memory structures, such as 3D NAND architecture semiconductor memory devices, are being developed to further increase memory density and lower memory cost.

Such 3D NAND devices often include strings of storage cells, coupled in series (e.g., drain to source), between one or more source-side select gates (SGSs) proximate a source, and one or more drain-side select gates (SGDs) proximate a bit line. In an example, the SGSs or the SGDs can include one or more field-effect transistors (FETs) or metal-oxide semiconductor (MOS) structure devices, etc. In some examples, the strings will extend vertically, through multiple vertically spaced tiers containing respective word lines. A semiconductor structure (e.g., a polysilicon structure) may extend adjacent a string of storage cells to form a channel for the storages cells of the string. In the example of a vertical string, the polysilicon structure may be in the form of a vertically extending pillar. In some examples the string may be “folded,” and thus arranged relative to a U-shaped pillar. In other examples, multiple vertical structures may be stacked upon one another to form stacked arrays of storage cell strings.

Memory arrays or devices can be combined together to form a storage volume of a memory system, such as a solid-state drive (SSD), a Universal Flash Storage (UFS™) device, a MultiMediaCard (MMC) solid-state storage device, an embedded MMC device (eMMC™), etc. An SSD can be used as, among other things, the main storage device of a computer, having advantages over traditional hard drives with moving parts with respect to, for example, performance, size, weight, ruggedness, operating temperature range, and power consumption. For example, SSDs can have reduced seek time, latency, or other delay associated with magnetic disk drives (e.g., electromechanical, etc.). SSDs use non-volatile memory cells, such as flash memory cells to obviate internal battery supply requirements, thus allowing the drive to be more versatile and compact.

An SSD can include a number of memory devices, including a number of dies or logical units (e.g., logical unit numbers or LUNs), and can include one or more processors or other controllers performing logic functions required to operate the memory devices or interface with external systems. Such SSDs may include one or more flash memory die, including a number of memory arrays and peripheral circuitry thereon. The flash memory arrays can include a number of blocks of memory cells organized into a number of physical pages. In many examples, the SSDs will also include DRAM or SRAM (or other forms of memory die or other memory structures). The SSD can receive commands from a host in association with memory operations, such as read or write operations to transfer data (e.g., user data and associated integrity data, such as error data and address data, etc.) between the memory devices and the host, or erase operations to erase data from the memory devices.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

FIG. 1 illustrates an example of an environment including a memory device.

FIGS. 2-3 illustrate schematic diagrams of an example of a 3D NAND architecture semiconductor memory array.

FIG. 4 illustrates an example block diagram of a memory module.

FIG. 5 illustrates a flowchart of an example of a method for encoding cells of a multi-level NAND.

FIG. 6 illustrates voltage distributions for a three-level encoding of a multi-level NAND.

FIG. 7 illustrates voltage distributions for a modified three-level encoding of a multi-level NAND.

FIG. 8 illustrates a flowchart of a method for NAND cell encoding to improve data integrity.

FIG. 9 is a block diagram illustrating an example of a machine upon which one or more embodiments may be implemented.

DETAILED DESCRIPTION

Flash devices operate by storing different charges on a device (e.g., floating gate). The stored charge interferes with a control gate to indicate a value stored in a cell. For example, in a single level cell, the read voltage of the control gate is calibrated to be between a charge for a ‘1’ bit and a charge for a ‘0’ bit; thus the read voltage is strong enough to overcome the ‘1’ charge and not strong enough to overcome the ‘0’ bit charge. For multi-level-cells (MLCs) of two bits or three bits, the floating gate charge may have many states (e.g., four and eight respectively) to represent two or three bits at each state.

Charge accumulation and dissipation from the cells varies with temperature. Higher read errors due to different write and read temperature (e.g., a write at 40c and read at 109 C and vice versa) are related to the unequal Vt distribution shifts between the NAND cell voltage and the read voltages (e.g., which may be compensated internally by the device). This is known as a cross-temperature, where the charge on the cell crosses a read boundary due to the temperature. In some cases, the cross-temperature situation may result in voltage distribution widening due to non-uniform cross-temperature response of each cell in a page.

High temperature situations may occur in some environments, such as in industrial machinery. They may also occur at specific times in the life-cycle of the device. For example, a device may be manufactured with data (e.g., firmware, boot code, etc.) and shipped to an integration manufacturer. The device package may then be attached to a finished component and subjected to solder re-flow to ensure the package's electrical connections. This solder re-flow (e.g., 3×IR reflow) may subject the cells to a high temperature and induce errors.

To address these issues, a modified encoding is proposed for increasing voltage read window budget while also maintaining an acceptable capacity for the device. Three level cell (TLC) margins are generally too narrow to support cross-temperature retention requirements across the extreme temperature range (e.g., −40 C to 109 C). Even with take a significant tPROG impact to provide greater margins, traditional TLC will likely fail under this extreme temperature requirement. Transitioning to an SLC may provide the margins to address the large temperature swing, but often sacrifices too much storage capacity to be desirable by customers. Therefore, writing user data in a four-level distribution using eight-level voltage distributions when the drive is operating outside the nominal temperature range will help to meet cross temperature retention requirement while providing increased capacity over an SLC encoding. Thus, 4 states are programmed in eight-state window distributions to increase read window budget (RWB) margins for extreme temperature programming. This technique does not impact programming time but instead of storing three bits for each cell, two bits are stored for each cell, allowing the device to keep data up to 66% of its TLC capacity with corrupting in high-temperature situations. Additional details and examples are provided below.

Electronic devices, such as mobile electronic devices (e.g., smart phones, tablets, etc.), electronic devices for use in automotive applications (e.g., automotive sensors, control units, driver-assistance systems, passenger safety or comfort systems, etc.), and internet-connected appliances or devices (e.g., internet-of-things (IoT) devices, etc.), have varying storage needs depending on, among other things, the type of electronic device, use environment, performance expectations, etc.

Electronic devices can be broken down into several main components: a processor (e.g., a central processing unit (CPU) or other main processor); memory (e.g., one or more volatile or non-volatile random-access memory (RAM) memory device, such as dynamic RAM (DRAM), mobile or low-power double-data-rate synchronous DRAM (DDR SDRAM), etc.); and a storage device (e.g., non-volatile memory (NVM) device, such as flash memory, read-only memory (ROM), an SSD, an MMC, or other memory card structure or assembly, etc.). In certain examples, electronic devices can include a user interface (e.g., a display, touch-screen, keyboard, one or more buttons, etc.), a graphics processing unit (GPU), a power management circuit, a baseband processor or one or more transceiver circuits, etc.

FIG. 1 illustrates an example of an environment 100 including a host device 105 and a memory device 110 configured to communicate over a communication interface. The host device 105 or the memory device 110 may be included in a variety of products 150, such as Internet of Things (IoT) devices (e.g., a refrigerator or other appliance, sensor, motor or actuator, mobile communication device, automobile, drone, etc.) to support processing, communications, or control of the product 150.

The memory device 110 includes a memory controller 115 and a memory array 120 including, for example, a number of individual memory die (e.g., a stack of three-dimensional (3D) NAND die). In 3D architecture semiconductor memory technology, vertical structures are stacked, increasing the number of tiers, physical pages, and accordingly, the density of a memory device (e.g., a storage device). In an example, the memory device 110 can be a discrete memory or storage device component of the host device 105. In other examples, the memory device 110 can be a portion of an integrated circuit (e.g., system on a chip (SOC), etc.), stacked or otherwise included with one or more other components of the host device 105.

One or more communication interfaces can be used to transfer data between the memory device 110 and one or more other components of the host device 105, such as a Serial Advanced Technology Attachment (SATA) interface, a Peripheral Component Interconnect Express (PCIe) interface, a Universal Serial Bus (USB) interface, a Universal Flash Storage (UFS) interface, an eMMC™ interface, or one or more other connectors or interfaces. The host device 105 can include a host system, an electronic device, a processor, a memory card reader, or one or more other electronic devices external to the memory device 110. In some examples, the host 105 may be a machine having some portion, or all, of the components discussed in reference to the machine 900 of FIG. 9.

The memory controller 115 can receive instructions from the host 105, and can communicate with the memory array, such as to transfer data to (e.g., write or erase) or from (e.g., read) one or more of the memory cells, planes, sub-blocks, blocks, or pages of the memory array. The memory controller 115 can include, among other things, circuitry or firmware, including one or more components or integrated circuits. For example, the memory controller 115 can include one or more memory control units, circuits, or components configured to control access across the memory array 120 and to provide a translation layer between the host 105 and the memory device 110. The memory controller 115 can include one or more input/output (I/O) circuits, lines, or interfaces to transfer data to or from the memory array 120. The memory controller 115 can include a memory manager 125 and an array controller 135.

The memory manager 125 can include, among other things, circuitry or firmware, such as a number of components or integrated circuits associated with various memory management functions. For purposes of the present description example memory operation and management functions will be described in the context of NAND memory. Persons skilled in the art will recognize that other forms of non-volatile memory may have analogous memory operations or management functions. Such NAND management functions include wear leveling (e.g., garbage collection or reclamation), error detection or correction, block retirement, or one or more other memory management functions. The memory manager 125 can parse or format host commands (e.g., commands received from a host) into device commands (e.g., commands associated with operation of a memory array, etc.), or generate device commands (e.g., to accomplish various memory management functions) for the array controller 135 or one or more other components of the memory device 110.

The memory manager 125 can include a set of management tables 130 configured to maintain various information associated with one or more component of the memory device 110 (e.g., various information associated with a memory array or one or more memory cells coupled to the memory controller 115). For example, the management tables 130 can include information regarding block age, block erase count, error history, or one or more error counts (e.g., a write operation error count, a read bit error count, a read operation error count, an erase error count, etc.) for one or more blocks of memory cells coupled to the memory controller 115. In certain examples, if the number of detected errors for one or more of the error counts is above a threshold, the bit error can be referred to as an uncorrectable bit error. The management tables 130 can maintain a count of correctable or uncorrectable bit errors, among other things.

The array controller 135 can include, among other things, circuitry or components configured to control memory operations associated with writing data to, reading data from, or erasing one or more memory cells of the memory device 110 coupled to the memory controller 115. The memory operations can be based on, for example, host commands received from the host 105, or internally generated by the memory manager 125 (e.g., in association with wear leveling, error detection or correction, etc.).

The array controller 135 can include an error correction code (ECC) component 140, which can include, among other things, an ECC engine or other circuitry configured to detect or correct errors associated with writing data to or reading data from one or more memory cells of the memory device 110 coupled to the memory controller 115. The memory controller 115 can be configured to actively detect and recover from error occurrences (e.g., bit errors, operation errors, etc.) associated with various operations or storage of data, while maintaining integrity of the data transferred between the host 105 and the memory device 110, or maintaining integrity of stored data (e.g., using redundant RAID storage, etc.), and can remove (e.g., retire) failing memory resources (e.g., memory cells, memory arrays, pages, blocks, etc.) to prevent future errors.

The memory array 120 can include several memory cells arranged in, for example, a number of devices, planes, sub-blocks, blocks, or pages. As one example, a 48 GB TLC NAND memory device can include 18,592 bytes (B) of data per page (16,384+2208 bytes), 1536 pages per block, 548 blocks per plane, and 4 or more planes per device. As another example, a 32 GB MLC memory device (storing two bits of data per cell (i.e., 4 programmable states)) can include 18,592 bytes (B) of data per page (16,384+2208 bytes), 1024 pages per block, 548 blocks per plane, and 4 planes per device, but with half the required write time and twice the program/erase (P/E) cycles as a corresponding TLC memory device. Other examples can include other numbers or arrangements. In some examples, a memory device, or a portion thereof, may be selectively operated in SLC mode, or in a desired MLC mode (such as TLC, QLC, etc.).

In operation, data is typically written to or read from the NAND memory device 110 in pages, and erased in blocks. However, one or more memory operations (e.g., read, write, erase, etc.) can be performed on larger or smaller groups of memory cells, as desired. The data transfer size of a NAND memory device 110 is typically referred to as a page, whereas the data transfer size of a host is typically referred to as a sector.

Although a page of data can include a number of bytes of user data (e.g., a data payload including a number of sectors of data) and its corresponding metadata, the size of the page often refers only to the number of bytes used to store the user data. As an example, a page of data having a page size of 4 KB may include 4 KB of user data (e.g., 8 sectors assuming a sector size of 512 B) as well as a number of bytes (e.g., 32 B, 54 B, 224 B, etc.) of metadata corresponding to the user data, such as integrity data (e.g., error detecting or correcting code data), address data (e.g., logical address data, etc.), or other metadata associated with the user data.

Different types of memory cells or memory arrays 120 can provide for different page sizes, or may require different amounts of metadata associated therewith. For example, different memory device types may have different bit error rates, which can lead to different amounts of metadata necessary to ensure integrity of the page of data (e.g., a memory device with a higher bit error rate may require more bytes of error correction code data than a memory device with a lower bit error rate). As an example, a multi-level cell (MLC) NAND flash device may have a higher bit error rate than a corresponding single-level cell (SLC) NAND flash device. As such, the MLC device may require more metadata bytes for error data than the corresponding SLC device.

To address high-temperature situations, the memory controller 115 is further arranged to obtain (e.g., retrieve or receive) a high-temperature indicator and arranged to receive a write operation. The memory controller 115 is arranged to perform the write operation on a NAND cell using a modified encoding in response to the high-temperature indicator. As used herein, encoding refers to a mapping between an observable state of the cell and a bit representation. Thus, in an SLC cell, the encoding is a ‘1’ for a charge below the read voltage and a ‘0’ for a charge above the read voltage. In an example, the modified encoding includes a reduced number of voltage distribution positions from an unmodified encoding without changing voltage distribution widths. Here, the position of a voltage distribution is defined as a central tendency of a range of voltages bounded by values within half of a width of the central tendency. Each voltage distribution corresponds to a discrete set of states an encoding. FIG. 6 illustrates such a TLC encoding with voltage positions and corresponding bit representations.

In an example, the modified encoding includes changing a voltage distribution position from a first position in the unmodified encoding to a second position in the modified encoding. In this example, the actual target voltage for a given encoding position is modified (e.g., trimmed) up or down from its place on the unmodified encoding. These trims may further increase read margins. In an example, the second position is within a defined range of voltages. In an example, the range of voltages is set defined by a read voltage for a state in the discrete set of states for the unmodified encoding that corresponds to the voltage distribution position. These examples constrain the voltage position shift such that an unmodified encoding read still works correctly on the modified encoded data. Thus, read voltages do not have to change to read the modified encoded data. In an example, the second position increases a read margin for the voltage distribution.

In an example, the unmodified encoding has eight discrete states (e.g., TLC). In an example, the modified encoding has four discrete states (e.g., a voltage position reduction of four from the unmodified encoding). In an example, the four discrete states correspond to states three, four, and seven from the eight discrete states, the states ordered by voltage from lower to higher. In an example, the voltage distribution position for state three is moved downward. In an example, the voltage distribution position for seven is moved downward. In an example, the voltage distribution position for state four is moved upward. These examples illustrate a modified TLC encoding in which read margins are maximized without modifying the TLC read voltages.

In an example, the unmodified encoding has four discrete states. In an example, the modified encoding has two discrete states. This encoding has SLC capacity but increases read margins even further.

In an example, the write operation is performed in two passes. In an example, the first pass operates in accordance with parameters of the unmodified encoding and the second pass operates to enact the modified encoding. In an example, the first pass writes a lower page. Thus, the lower page of the TLC encoding is written in the same manner as the unmodified TLC encoding. However, the second pass effectuates the modified encoding by limiting the number of intermediate voltage states available for the programming.

As noted above, the modified encoding does not affect the reading of the data with respect to read voltages. Thus, the controller 115 is arranged perform a read operation on the cell using the unmodified encoding. In an example, the XP page may be ignored during the read.

The memory controller 115 may also be arranged to obtain clearance of the high-temperature indicator and perform maintenance on the cell to free the NAND cell for another write operation. Subsequently, a second write operation may be received and the second write operation may be performed on the cell using the unmodified encoding in response to clearance of the high-temperature indicator. Thus, once the high-temperature condition has passed, the cell may be used with the unmodified encoding, thus increasing utilization.

FIG. 2 illustrates an example schematic diagram of a 3D NAND architecture semiconductor memory array 200 including a number of strings of memory cells (e.g., first-third A₀ memory strings 205A₀-207A₀, first-third A_(n) memory strings 205A_(n)-207A_(n), first-third B₀ memory strings 205B₀-207B₀, first-third B_(n) memory strings 205B_(n)-207B_(n), etc.), organized in blocks (e.g., block A 201A, block B 201B, etc.) and sub-blocks (e.g., sub-block A₀ 201A₀, sub-block A_(n) 201A_(n), sub-block B₀ 201B₀, sub-block B_(n) 201B_(n), etc.). The memory array 200 represents a portion of a greater number of similar structures that would typically be found in a block, device, or other unit of a memory device.

Each string of memory cells includes a number of tiers of charge storage transistors (e.g., floating gate transistors, charge-trapping structures, etc.) stacked in the Z direction, source to drain, between a source line (SRC) 235 or a source-side select gate (SGS) (e.g., first-third A₀ SGS 231A₀-233A₀, first-third A_(n) SGS 231A_(n)-233A_(n), first-third B₀ SGS 231B₀-233B₀, first-third B_(n) SGS 231B_(n)-233B_(n), etc.) and a drain-side select gate (SGD) (e.g., first-third A₀ SGD 226A₀-228A₀, first-third A_(n) SGD 226A_(n)-228A_(n), first-third B₀ SGD 226B₀-228B₀, first-third B_(n) SGD 226B_(n)-228B_(n), etc.). Each string of memory cells in the 3D memory array can be arranged along the X direction as data lines (e.g., bit lines (BL) BL0-BL2 220-222), and along the Y direction as physical pages.

Within a physical page, each tier represents a row of memory cells, and each string of memory cells represents a column. A sub-block can include one or more physical pages. A block can include a number of sub-blocks (or physical pages) (e.g., 128, 256, 384, etc.). Although illustrated herein as having two blocks, each block having two sub-blocks, each sub-block having a single physical page, each physical page having three strings of memory cells, and each string having 8 tiers of memory cells, in other examples, the memory array 200 can include more or fewer blocks, sub-blocks, physical pages, strings of memory cells, memory cells, or tiers. For example, each string of memory cells can include more or fewer tiers (e.g., 16, 32, 64, 128, etc.), as well as one or more additional tiers of semiconductor material above or below the charge storage transistors (e.g., select gates, data lines, etc.), as desired. As an example, a 48 GB TLC NAND memory device can include 18,592 bytes (B) of data per page (16,384+2208 bytes), 1536 pages per block, 548 blocks per plane, and 4 or more planes per device.

Each memory cell in the memory array 200 includes a control gate (CG) coupled to (e.g., electrically or otherwise operatively connected to) an access line (e.g., word lines (WL) WL0 ₀-WL7 ₀ 210A-217A, WL0 ₁-WL7 ₁ 210B-217B, etc.), which collectively couples the control gates (CGs) across a specific tier, or a portion of a tier, as desired. Specific tiers in the 3D memory array, and accordingly, specific memory cells in a string, can be accessed or controlled using respective access lines. Groups of select gates can be accessed using various select lines. For example, first-third A₀ SGD 226A₀-228A₀ can be accessed using an A₀ SGD line SGDA₀ 225A₀, first-third A_(n) SGD 226A_(n)-228A_(n) can be accessed using an A_(n) SGD line SGDA_(n) 225A_(n), first-third B₀ SGD 226B₀-228B₀ can be accessed using an B₀ SGD line SGDB₀ 225B₀, and first-third B SGD 226B_(n)-228B_(n) can be accessed using an B_(n) SGD line SGDB_(n) 225B_(n). First-third A₀ SGS 231A₀-233A₀ and first-third A_(n) SGS 231A_(n)-233A_(n) can be accessed using a gate select line SGS₀ 230A, and first-third B₀ SGS 231B₀-233B₀ and first-third B_(n) SGS 231B_(n)-233B_(n) can be accessed using a gate select line SGS₁ 230B.

In an example, the memory array 200 can include a number of levels of semiconductor material (e.g., polysilicon, etc.) configured to couple the control gates (CGs) of each memory cell or select gate (or a portion of the CGs or select gates) of a respective tier of the array. Specific strings of memory cells in the array can be accessed, selected, or controlled using a combination of bit lines (BLs) and select gates, etc., and specific memory cells at one or more tiers in the specific strings can be accessed, selected, or controlled using one or more access lines (e.g., word lines).

FIG. 3 illustrates an example schematic diagram of a portion of a NAND architecture semiconductor memory array 300 including a plurality of memory cells 302 arranged in a two-dimensional array of strings (e.g., first-third strings 305-307) and tiers (e.g., illustrated as respective word lines (WL) WL0-WL7 310-317, a drain-side select gate (SGD) line 325, a source-side select gate (SGS) line 330, etc.), and sense amplifiers or devices 360. For example, the memory array 300 can illustrate an example schematic diagram of a portion of one physical page of memory cells of a 3D NAND architecture semiconductor memory device, such as illustrated in FIG. 2.

Each string of memory cells is coupled to a source line (SRC) using a respective source-side select gate (SGS) (e.g., first-third SGS 331-333), and to a respective data line (e.g., first-third bit lines (BL) BL0-BL2 320-322) using a respective drain-side select gate (SGD) (e.g., first-third SGD 326-328). Although illustrated with 8 tiers (e.g., using word lines (WL) WL0-WL7 310-317) and three data lines (BL0-BL2 326-328) in the example of FIG. 3, other examples can include strings of memory cells having more or fewer tiers or data lines, as desired.

In a NAND architecture semiconductor memory array, such as the example memory array 300, the state of a selected memory cell 302 can be accessed by sensing a current or voltage variation associated with a particular data line containing the selected memory cell. The memory array 300 can be accessed (e.g., by a control circuit, one or more processors, digital logic, etc.) using one or more drivers. In an example, one or more drivers can activate a specific memory cell, or set of memory cells, by driving a particular potential to one or more data lines (e.g., bit lines BL0-BL2), access lines (e.g., word lines WL0-WL7), or select gates, depending on the type of operation desired to be performed on the specific memory cell or set of memory cells.

To program or write data to a memory cell, a programming voltage (Vpgm) (e.g., one or more programming pulses, etc.) can be applied to selected word lines (e.g., WL4), and thus, to a control gate of each memory cell coupled to the selected word lines (e.g., first-third control gates (CGs) 341-343 of the memory cells coupled to WL4). Programming pulses can begin, for example, at or near 15V, and, in certain examples, can increase in magnitude during each programming pulse application. While the program voltage is applied to the selected word lines, a potential, such as a ground potential (e.g., Vss), can be applied to the data lines (e.g., bit lines) and substrates (and thus the channels, between the sources and drains) of the memory cells targeted for programming, resulting in a charge transfer (e.g., direct injection or Fowler-Nordheim (FN) tunneling, etc.) from the channels to the floating gates of the targeted memory cells.

In contrast, a pass voltage (Vpass) can be applied to one or more word lines having memory cells that are not targeted for programming, or an inhibit voltage (e.g., Vcc) can be applied to data lines (e.g., bit lines) having memory cells that are not targeted for programming, for example, to inhibit charge from being transferred from the channels to the floating gates of such non-targeted memory cells. The pass voltage can be variable, depending, for example, on the proximity of the applied pass voltages to a word line targeted for programming. The inhibit voltage can include a supply voltage (Vcc), such as a voltage from an external source or supply (e.g., a battery, an AC-to-DC converter, etc.), relative to a ground potential (e.g., Vss).

As an example, if a programming voltage (e.g., 15V or more) is applied to a specific word line, such as WL4, a pass voltage of 10V can be applied to one or more other word lines, such as WL3, WL5, etc., to inhibit programming of non-targeted memory cells, or to retain the values stored on such memory cells not targeted for programming. As the distance between an applied program voltage and the non-targeted memory cells increases, the pass voltage required to refrain from programming the non-targeted memory cells can decrease. For example, where a programming voltage of 15V is applied to WL4, a pass voltage of 10V can be applied to WL3 and WL5, a pass voltage of 8V can be applied to WL2 and WL6, a pass voltage of 7V can be applied to WL1 and WL7, etc. In other examples, the pass voltages, or number of word lines, etc., can be higher or lower, or more or less.

The sense amplifiers 360, coupled to one or more of the data lines (e.g., first, second, or third bit lines (BL0-BL2) 320-322), can detect the state of each memory cell in respective data lines by sensing a voltage or current on a particular data line.

Between applications of one or more programming pulses (e.g., Vpgm), a verify operation can be performed to determine if a selected memory cell has reached its intended programmed state. If the selected memory cell has reached its intended programmed state, it can be inhibited from further programming. If the selected memory cell has not reached its intended programmed state, additional programming pulses can be applied. If the selected memory cell has not reached its intended programmed state after a particular number of programming pulses (e.g., a maximum number), the selected memory cell, or a string, block, or page associated with such selected memory cell, can be marked as defective.

To erase a memory cell or a group of memory cells (e.g., erasure is typically performed in blocks or sub-blocks), an erasure voltage (Vers) (e.g., typically Vpgm) can be applied to the substrates (and thus the channels, between the sources and drains) of the memory cells targeted for erasure (e.g., using one or more bit lines, select gates, etc.), while the word lines of the targeted memory cells are kept at a potential, such as a ground potential (e.g., Vss), resulting in a charge transfer (e.g., direct injection or Fowler-Nordheim (FN) tunneling, etc.) from the floating gates of the targeted memory cells to the channels.

FIG. 4 illustrates an example block diagram of a memory device 400 including a memory array 402 having a plurality of memory cells 404, and one or more circuits or components to provide communication with, or perform one or more memory operations on, the memory array 402. The memory device 400 can include a row decoder 412, a column decoder 414, sense amplifiers 420, a page buffer 422, a selector 424, an input/output (I/O) circuit 426, and a memory control unit 430.

The memory cells 404 of the memory array 402 can be arranged in blocks, such as first and second blocks 402A, 402B. Each block can include sub-blocks. For example, the first block 402A can include first and second sub-blocks 402A₀, 402A_(n), and the second block 402B can include first and second sub-blocks 402B₀, 402B_(n). Each sub-block can include a number of physical pages, each page including a number of memory cells 404. Although illustrated herein as having two blocks, each block having two sub-blocks, and each sub-block having a number of memory cells 404, in other examples, the memory array 402 can include more or fewer blocks, sub-blocks, memory cells, etc. In other examples, the memory cells 404 can be arranged in a number of rows, columns, pages, sub-blocks, blocks, etc., and accessed using, for example, access lines 406, first data lines 410, or one or more select gates, source lines, etc.

The memory control unit 430 can control memory operations of the memory device 400 according to one or more signals or instructions received on control lines 432, including, for example, one or more clock signals or control signals that indicate a desired operation (e.g., write, read, erase, etc.), or address signals (A0-AX) received on one or more address lines 416. One or more devices external to the memory device 400 can control the values of the control signals on the control lines 432, or the address signals on the address line 416. Examples of devices external to the memory device 400 can include, but are not limited to, a host, a memory controller, a processor, or one or more circuits or components not illustrated in FIG. 4.

The memory device 400 can use access lines 406 and first data lines 410 to transfer data to (e.g., write or erase) or from (e.g., read) one or more of the memory cells 404. The row decoder 412 and the column decoder 414 can receive and decode the address signals (A0-AX) from the address line 416, can determine which of the memory cells 404 are to be accessed, and can provide signals to one or more of the access lines 406 (e.g., one or more of a plurality of word lines (WL0-WLm)) or the first data lines 410 (e.g., one or more of a plurality of bit lines (BL0-BLn)), such as described above.

The memory device 400 can include sense circuitry, such as the sense amplifiers 420, configured to determine the values of data on (e.g., read), or to determine the values of data to be written to, the memory cells 404 using the first data lines 410. For example, in a selected string of memory cells 404, one or more of the sense amplifiers 420 can read a logic level in the selected memory cell 404 in response to a read current flowing in the memory array 402 through the selected string to the data lines 410.

One or more devices external to the memory device 400 can communicate with the memory device 400 using the I/O lines (DQ0-DQN) 408, address lines 416 (A0-AX), or control lines 432. The input/output (I/O) circuit 426 can transfer values of data in or out of the memory device 400, such as in or out of the page buffer 422 or the memory array 402, using the I/O lines 408, according to, for example, the control lines 432 and address lines 416. The page buffer 422 can store data received from the one or more devices external to the memory device 400 before the data is programmed into relevant portions of the memory array 402, or can store data read from the memory array 402 before the data is transmitted to the one or more devices external to the memory device 400.

The column decoder 414 can receive and decode address signals (A0-AX) into one or more column select signals (CSEL1-CSELn). The selector 424 (e.g., a select circuit) can receive the column select signals (CSEL1-CSELn) and select data in the page buffer 422 representing values of data to be read from or to be programmed into memory cells 404. Selected data can be transferred between the page buffer 422 and the I/O circuit 426 using second data lines 418.

The memory control unit 430 can receive positive and negative supply signals, such as a supply voltage (Vcc) 434 and a negative supply (Vss) 436 (e.g., a ground potential), from an external source or supply (e.g., an internal or external battery, an AC-to-DC converter, etc.). In certain examples, the memory control unit 430 can include a regulator 428 to internally provide positive or negative supply signals.

FIG. 5 illustrates a flowchart of an example of a method 500 for encoding cells of a multi-level NAND. The operations of the method 500 are performed by hardware, such as that described above with respect to FIGS. 1-4 and below with respect to FIG. 9 (e.g., processing circuitry). When the cell is being written, the first pass (e.g., lower page or LP) is written in the traditional manner. Afterwards, if there is no high-temperature situation (decision 505), the second pass programming proceeds as normal (operation 510). However, if there is a high-temperature situation (decision 505), the modified encoding is enacted. First, trim settings are retrieved (operation 515) These trim settings define a difference between a traditional voltage for a given encoding position and the modified encoding. The user data is then marshalled (operation 520) and written (operation 525) in accordance with the modified encoding. The trims may then be reset (operation 530) and the block marked for maintenance (535). Thus, first pass programming programs LP as usual with default trims. The second pass programming may adjust PV3 downward. PV4 upward, and PV7 downward to provide more margins for cross-temperature situations. Host data may be loaded on the UP page, and the final page (XP) receives a ‘1’. The programming time and read time are similar to TLC. As noted above, reading involves a normal TLC read regardless of 8-state or 4-state encoding. However, of the data read, valid data is restricted to the LP and UP pages (XP has dummy data).

FIG. 6 illustrates voltage distributions for a three-level encoding of a multi-level NAND. The distributions illustrate the eight voltage values corresponding to eight encoding states. The order in which the data is encoded in the multiple programming passes is noted from the top to the bottom and by arrows indicating how voltage is added at each stage of the programming to achieve the subsequent state. The read voltages for the pages are indicated by the shade-coordinated arrows on the bottom line. FIG. 6 represents an unmodified TLC encoding.

FIG. 7 illustrates voltage distributions for a modified three-level encoding of a multi-level NAND. The encoding illustrated in FIG. 7 represents a modified encoding of the TLC encoding illustrated in FIG. 6. Here, the PV arrows on the bottom line indicate voltages of the TLC states. Note that positions PV011, PV001, PV000, and PV010 do not have voltages in the modified encoding; these positions are eliminated. Note that the position PV101 differs from the center of L3. Here, the trim on PV101 has been adjusted upwards. As noted above, the XP pages have the same data, ‘1’. Thus, the valid bits are held in the LP and UP pages.

FIG. 8 illustrates a flowchart of a method 800 for NAND cell encoding to improve data integrity. The operations of the method 800 are performed by hardware, such as that described above with respect to FIGS. 1-4 and below with respect to FIG. 9 (e.g., processing circuitry).

At operation 805, a high-temperature indicator is obtained.

At operation 820, a write operation is received.

At operation 815, the write operation is performed on a NAND cell using a modified encoding in response to the high-temperature indicator. In an example, the modified encoding includes a reduced number of voltage distribution positions from an unmodified encoding without changing voltage distribution widths. Here, the position of a voltage distribution is defined as a central tendency of a range of voltages bounded by values within half of a width of the central tendency. Each voltage distribution corresponds to a discrete set of states an encoding.

In an example, the modified encoding includes changing a voltage distribution position from a first position in the unmodified encoding to a second position in the modified encoding. In an example, the second position is within a defined range of voltages. In an example, the range of voltages is set defined by a read voltage for a state in the discrete set of states for the unmodified encoding that corresponds to the voltage distribution position. In an example, the second position increases a read margin for the voltage distribution.

In an example, the unmodified encoding has eight discrete states. In an example, the modified encoding has four discrete states. In an example, the four discrete states correspond to states three, four, and seven from the eight discrete states, the states ordered by voltage from lower to higher. In an example, the voltage distribution position for state three is moved downward. In an example, the voltage distribution position for seven is moved downward. In an example, the voltage distribution position for state four is moved upward.

In an example, the unmodified encoding has four discrete states. In an example, the modified encoding has two discrete states.

In an example, the write operation is performed in two passes. In an example, the first pass operates in accordance with parameters of the unmodified encoding and the second pass operates to enact the modified encoding. In an example, the first pass writes a lower page.

In an example, the method 900 may be extended to perform a read operation on the NAND cell using the unmodified encoding.

In an example, the method 900 may be extended to obtain clearance of the high-temperature indicator and perform maintenance on the NAND cell to free the NAND cell for another write operation. Subsequently, a second write operation may be received and the second write operation may be performed on the NAND cell using the unmodified encoding in response to clearance of the high-temperature indicator.

FIG. 9 illustrates a block diagram of an example machine 900 upon which any one or more of the techniques (e.g., methodologies) discussed herein may perform. In alternative embodiments, the machine 900 may operate as a standalone device or may be connected (e.g., networked) to other machines. In a networked deployment, the machine 900 may operate in the capacity of a server machine, a client machine, or both in server-client network environments. In an example, the machine 900 may act as a peer machine in peer-to-peer (P2P) (or other distributed) network environment. The machine 900 may be a personal computer (PC), a tablet PC, a set-top box (STB), a personal digital assistant (PDA), a mobile telephone, a web appliance, an IoT device, automotive system, or any machine capable of executing instructions (sequential or otherwise) that specify actions to be taken by that machine. Further, while only a single machine is illustrated, the term “machine” shall also be taken to include any collection of machines that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein, such as cloud computing, software as a service (SaaS), other computer cluster configurations.

Examples, as described herein, may include, or may operate by, logic, components, devices, packages, or mechanisms. Circuitry is a collection (e.g., set) of circuits implemented in tangible entities that include hardware (e.g., simple circuits, gates, logic, etc.). Circuitry membership may be flexible over time and underlying hardware variability. Circuitries include members that may, alone or in combination, perform specific tasks when operating. In an example, hardware of the circuitry may be immutably designed to carry out a specific operation (e.g., hardwired). In an example, the hardware of the circuitry may include variably connected physical components (e.g., execution units, transistors, simple circuits, etc.) including a computer readable medium physically modified (e.g., magnetically, electrically, moveable placement of invariant massed particles, etc.) to encode instructions of the specific operation. In connecting the physical components, the underlying electrical properties of a hardware constituent are changed, for example, from an insulator to a conductor or vice versa. The instructions enable participating hardware (e.g., the execution units or a loading mechanism) to create members of the circuitry in hardware via the variable connections to carry out portions of the specific tasks when in operation. Accordingly, the computer readable medium is communicatively coupled to the other components of the circuitry when the device is operating. In an example, any of the physical components may be used in more than one member of more than one circuitry. For example, under operation, execution units may be used in a first circuit of a first circuitry at one point in time and reused by a second circuit in the first circuitry, or by a third circuit in a second circuitry at a different time.

The machine (e.g., computer system) 900 (e.g., the host device 105, the memory device 110, etc.) may include a hardware processor 902 (e.g., a central processing unit (CPU), a graphics processing unit (GPU), a hardware processor core, or any combination thereof, such as the memory controller 115, etc.), a main memory 904 and a static memory 906, some or all of which may communicate with each other via an interlink (e.g., bus) 908. The machine 900 may further include a display unit 910, an alphanumeric input device 912 (e.g., a keyboard), and a user interface (UI) navigation device 914 (e.g., a mouse). In an example, the display unit 910, input device 912 and UI navigation device 914 may be a touch screen display. The machine 900 may additionally include a storage device (e.g., drive unit) 916, a signal generation device 918 (e.g., a speaker), a network interface device 920, and one or more sensors 916, such as a global positioning system (GPS) sensor, compass, accelerometer, or other sensor. The machine 900 may include an output controller 928, such as a serial (e.g., universal serial bus (USB), parallel, or other wired or wireless (e.g., infrared (IR), near field communication (NFC), etc.) connection to communicate or control one or more peripheral devices (e.g., a printer, card reader, etc.).

The storage device 916 may include a machine readable medium 922 on which is stored one or more sets of data structures or instructions 924 (e.g., software) embodying or utilized by any one or more of the techniques or functions described herein. The instructions 924 may also reside, completely or at least partially, within the main memory 904, within static memory 906, or within the hardware processor 902 during execution thereof by the machine 900. In an example, one or any combination of the hardware processor 902, the main memory 904, the static memory 906, or the storage device 916 may constitute the machine readable medium 922.

While the machine readable medium 922 is illustrated as a single medium, the term “machine readable medium” may include a single medium or multiple media (e.g., a centralized or distributed database, or associated caches and servers) configured to store the one or more instructions 924.

The term “machine readable medium” may include any medium that is capable of storing, encoding, or carrying instructions for execution by the machine 900 and that cause the machine 900 to perform any one or more of the techniques of the present disclosure, or that is capable of storing, encoding or carrying data structures used by or associated with such instructions. Non-limiting machine readable medium examples may include solid-state memories, and optical and magnetic media. In an example, a massed machine readable medium comprises a machine-readable medium with a plurality of particles having invariant (e.g., rest) mass. Accordingly, massed machine-readable media are not transitory propagating signals. Specific examples of massed machine readable media may include: non-volatile memory, such as semiconductor memory devices (e.g., Electrically Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM)) and flash memory devices; magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks.

The instructions 924 (e.g., software, programs, an operating system (OS), etc.) or other data are stored on the storage device 921, can be accessed by the memory 904 for use by the processor 902. The memory 904 (e.g., DRAM) is typically fast, but volatile, and thus a different type of storage than the storage device 921 (e.g., an SSD), which is suitable for long-term storage, including while in an “off” condition. The instructions 924 or data in use by a user or the machine 900 are typically loaded in the memory 904 for use by the processor 902. When the memory 904 is full, virtual space from the storage device 921 can be allocated to supplement the memory 904; however, because the storage 921 device is typically slower than the memory 904, and write speeds are typically at least twice as slow as read speeds, use of virtual memory can greatly reduce user experience due to storage device latency (in contrast to the memory 904, e.g., DRAM). Further, use of the storage device 921 for virtual memory can greatly reduce the usable lifespan of the storage device 921.

In contrast to virtual memory, virtual memory compression (e.g., the Linux™ kernel feature “ZRAM”) uses part of the memory as compressed block storage to avoid paging to the storage device 921. Paging takes place in the compressed block until it is necessary to write such data to the storage device 921. Virtual memory compression increases the usable size of memory 904, while reducing wear on the storage device 921.

Storage devices optimized for mobile electronic devices, or mobile storage, traditionally include MMC solid-state storage devices (e.g., micro Secure Digital (microSD™) cards, etc.). MMC devices include a number of parallel interfaces (e.g., an 8-bit parallel interface) with a host device, and are often removable and separate components from the host device. In contrast, eMMC™ devices are attached to a circuit board and considered a component of the host device, with read speeds that rival serial ATA™ (Serial AT (Advanced Technology) Attachment, or SATA) based SSD devices. However, demand for mobile device performance continues to increase, such as to fully enable virtual or augmented-reality devices, utilize increasing networks speeds, etc. In response to this demand, storage devices have shifted from parallel to serial communication interfaces. Universal Flash Storage (UFS) devices, including controllers and firmware, communicate with a host device using a low-voltage differential signaling (LVDS) serial interface with dedicated read/write paths, further advancing greater read/write speeds.

The instructions 924 may further be transmitted or received over a communications network 926 using a transmission medium via the network interface device 920 utilizing any one of a number of transfer protocols (e.g., frame relay, internet protocol (IP), transmission control protocol (TCP), user datagram protocol (UDP), hypertext transfer protocol (HTTP), etc.). Example communication networks may include a local area network (LAN), a wide area network (WAN), a packet data network (e.g., the Internet), mobile telephone networks (e.g., cellular networks), Plain Old Telephone (POTS) networks, and wireless data networks (e.g., Institute of Electrical and Electronics Engineers (IEEE) 802.11 family of standards known as Wi-Fi®, IEEE 802.16 family of standards known as WiMax™), IEEE 802.15.4 family of standards, peer-to-peer (P2P) networks, among others. In an example, the network interface device 920 may include one or more physical jacks (e.g., Ethernet, coaxial, or phone jacks) or one or more antennas to connect to the communications network 926. In an example, the network interface device 920 may include a plurality of antennas to wirelessly communicate using at least one of single-input multiple-output (SIMO), multiple-input multiple-output (MIMO), or multiple-input single-output (MISO) techniques. The term “transmission medium” shall be taken to include any intangible medium that is capable of storing, encoding or carrying instructions for execution by the machine 900, and includes digital or analog communications signals or other intangible medium to facilitate communication of such software.

ADDITIONAL EXAMPLES

Example 1 is a NAND device for NAND cell encoding, the NAND device comprising: a NAND cell; and a controller to: obtain a high-temperature indicator; receive a write operation; and perform the write operation on a NAND cell using a modified encoding in response to the high-temperature indicator, the modified encoding including a reduced number of voltage distribution positions from an unmodified encoding without changing voltage distribution widths, the position of a voltage distribution is defined as a central tendency of a range of voltages bounded by values within half of a width of the central tendency, each voltage distribution corresponding to a discrete set of states an encoding.

In Example 2, the subject matter of Example 1 includes, wherein the modified encoding includes a different voltage distribution position from a first position in the unmodified encoding to a second position in the modified encoding.

In Example 3, the subject matter of Example 2 includes, wherein the second position is within a defined range of voltages.

In Example 4, the subject matter of Examples 2-3 includes, wherein the range of voltages is set defined by a read voltage for a state in the discrete set of states for the unmodified encoding that corresponds to the voltage distribution position.

In Example 5, the subject matter of Examples 2-4 includes, wherein the second position increases a read margin for the voltage distribution.

In Example 6, the subject matter of Examples 1-5 includes, wherein the unmodified encoding has eight discrete states.

In Example 7, the subject matter of Example 6 includes, wherein the modified encoding has four discrete states.

In Example 8, the subject matter of Example 7 includes, wherein the write operation is performed in two passes, the first pass operating in accordance with parameters of the unmodified encoding, and the second pass operating to enact the modified encoding.

In Example 9, the subject matter of Example 8 includes, wherein the first pass writes a lower page.

In Example 10, the subject matter of Examples 8-9 includes, wherein the four discrete states correspond to states three, four, and seven from the eight discrete states, the states ordered by voltage from lower to higher.

In Example 11, the subject matter of Example 10 includes, wherein the voltage distribution position for state three is moved downward.

In Example 12, the subject matter of Examples 10-11 includes, wherein the voltage distribution position for seven is moved downward.

In Example 13, the subject matter of Examples 10-12 includes, wherein the voltage distribution position for state four is moved upward.

In Example 14, the subject matter of Examples 1-13 includes, wherein the unmodified encoding has four discrete states.

In Example 15, the subject matter of Example 14 includes, wherein the modified encoding has two discrete states.

In Example 16, the subject matter of Examples 1-15 includes, wherein the controller is arranged to perform a read operation on the NAND cell using the unmodified encoding.

In Example 17, the subject matter of Examples 1-16 includes, wherein the controller is arranged to: obtain a clearance of the high-temperature indicator; perform maintenance on the NAND cell to free the NAND cell for another write operation; receive a second write operation; and perform the second write operation on the NAND cell using the unmodified encoding in response to clearance of the high-temperature indicator.

Example 18 is a method for NAND cell encoding, the method comprising: obtaining a high-temperature indicator; receiving a write operation; and performing the write operation on a NAND cell using a modified encoding in response to the high-temperature indicator, the modified encoding including a reduced number of voltage distribution positions from an unmodified encoding without changing voltage distribution widths, the position of a voltage distribution is defined as a central tendency of a range of voltages bounded by values within half of a width of the central tendency, each voltage distribution corresponding to a discrete set of states an encoding.

In Example 19, the subject matter of Example 18 includes, wherein the modified encoding includes changing a voltage distribution position from a first position in the unmodified encoding to a second position in the modified encoding.

In Example 20, the subject matter of Example 19 includes, wherein the second position is within a defined range of voltages.

In Example 21, the subject matter of Examples 19-20 includes, wherein the range of voltages is set defined by a read voltage for a state in the discrete set of states for the unmodified encoding that corresponds to the voltage distribution position.

In Example 22, the subject matter of Examples 19-21 includes, wherein the second position increases a read margin for the voltage distribution.

In Example 23, the subject matter of Examples 18-22 includes, wherein the unmodified encoding has eight discrete states.

In Example 24, the subject matter of Example 23 includes, wherein the modified encoding has four discrete states.

In Example 25, the subject matter of Example 24 includes, wherein the write operation is performed in two passes, the first pass operating in accordance with parameters of the unmodified encoding, and the second pass operating to enact the modified encoding.

In Example 26, the subject matter of Example 25 includes, wherein the first pass writes a lower page.

In Example 27, the subject matter of Examples 25-26 includes, wherein the four discrete states correspond to states three, four, and seven from the eight discrete states, the states ordered by voltage from lower to higher.

In Example 28, the subject matter of Example 27 includes, wherein the voltage distribution position for state three is moved downward.

In Example 29, the subject matter of Examples 27-28 includes, wherein the voltage distribution position for seven is moved downward.

In Example 30, the subject matter of Examples 27-29 includes, wherein the voltage distribution position for state four is moved upward.

In Example 31, the subject matter of Examples 18-30 includes, wherein the unmodified encoding has four discrete states.

In Example 32, the subject matter of Example 31 includes, wherein the modified encoding has two discrete states.

In Example 33, the subject matter of Examples 18-32 includes, performing a read operation on the NAND cell using the unmodified encoding.

In Example 34, the subject matter of Examples 18-33 includes, obtaining a clearance of the high-temperature indicator; performing maintenance on the NAND cell to free the NAND cell for another write operation; receiving a second write operation; and performing the second write operation on the NAND cell using the unmodified encoding in response to clearance of the high-temperature indicator.

Example 35 is at least one machine readable medium including instructions that, when executed by processing circuitry, cause the processing circuitry to perform any method of Examples 18-34.

Example 36 is a system comprising means to perform any method of Examples 18-34.

Example 37 is at least one machine readable medium including instructions that, when executed by processing circuitry, cause the processing circuitry to perform operations comprising: obtaining a high-temperature indicator; receiving a write operation; and performing the write operation on a NAND cell using a modified encoding in response to the high-temperature indicator, the modified encoding including a reduced number of voltage distribution positions from an unmodified encoding without changing voltage distribution widths, the position of a voltage distribution is defined as a central tendency of a range of voltages bounded by values within half of a width of the central tendency, each voltage distribution corresponding to a discrete set of states an encoding.

In Example 38, the subject matter of Example 37 includes, wherein the modified encoding includes changing a voltage distribution position from a first position in the unmodified encoding to a second position in the modified encoding.

In Example 39, the subject matter of Example 38 includes, wherein the second position is within a defined range of voltages.

In Example 40, the subject matter of Examples 38-39 includes, wherein the range of voltages is set defined by a read voltage for a state in the discrete set of states for the unmodified encoding that corresponds to the voltage distribution position.

In Example 41, the subject matter of Examples 38-40 includes, wherein the second position increases a read margin for the voltage distribution.

In Example 42, the subject matter of Examples 37-41 includes, wherein the unmodified encoding has eight discrete states.

In Example 43, the subject matter of Example 42 includes, wherein the modified encoding has four discrete states.

In Example 44, the subject matter of Example 43 includes, wherein the write operation is performed in two passes, the first pass operating in accordance with parameters of the unmodified encoding, and the second pass operating to enact the modified encoding.

In Example 45, the subject matter of Example 44 includes, wherein the first pass writes a lower page.

In Example 46, the subject matter of Examples 44-45 includes, wherein the four discrete states correspond to states three, four, and seven from the eight discrete states, the states ordered by voltage from lower to higher.

In Example 47, the subject matter of Example 46 includes, wherein the voltage distribution position for state three is moved downward.

In Example 48, the subject matter of Examples 46-47 includes, wherein the voltage distribution position for seven is moved downward.

In Example 49, the subject matter of Examples 46-48 includes, wherein the voltage distribution position for state four is moved upward.

In Example 50, the subject matter of Examples 37-49 includes, wherein the unmodified encoding has four discrete states.

In Example 51, the subject matter of Example 50 includes, wherein the modified encoding has two discrete states.

In Example 52, the subject matter of Examples 37-51 includes, wherein the operations comprise performing a read operation on the NAND cell using the unmodified encoding.

In Example 53, the subject matter of Examples 37-52 includes, wherein the operations comprise: obtaining a clearance of the high-temperature indicator; performing maintenance on the NAND cell to free the NAND cell for another write operation; receiving a second write operation; and performing the second write operation on the NAND cell using the unmodified encoding in response to clearance of the high-temperature indicator.

Example 54 is a system for NAND cell encoding, the system comprising: means for obtaining a high-temperature indicator; means for receiving a write operation; and means for performing the write operation on a NAND cell using a modified encoding in response to the high-temperature indicator, the modified encoding including a reduced number of voltage distribution positions from an unmodified encoding without changing voltage distribution widths, the position of a voltage distribution is defined as a central tendency of a range of voltages bounded by values within half of a width of the central tendency, each voltage distribution corresponding to a discrete set of states an encoding.

In Example 55, the subject matter of Example 54 includes, wherein the modified encoding includes changing a voltage distribution position from a first position in the unmodified encoding to a second position in the modified encoding.

In Example 56, the subject matter of Example 55 includes, wherein the second position is within a defined range of voltages.

In Example 57, the subject matter of Examples 55-56 includes, wherein the range of voltages is set defined by a read voltage for a state in the discrete set of states for the unmodified encoding that corresponds to the voltage distribution position.

In Example 58, the subject matter of Examples 55-57 includes, wherein the second position increases a read margin for the voltage distribution.

In Example 59, the subject matter of Examples 54-58 includes, wherein the unmodified encoding has eight discrete states.

In Example 60, the subject matter of Example 59 includes, wherein the modified encoding has four discrete states.

In Example 61, the subject matter of Example 60 includes, wherein the write operation is performed in two passes, the first pass operating in accordance with parameters of the unmodified encoding, and the second pass operating to enact the modified encoding.

In Example 62, the subject matter of Example 61 includes, wherein the first pass writes a lower page.

In Example 63, the subject matter of Examples 61-62 includes, wherein the four discrete states correspond to states three, four, and seven from the eight discrete states, the states ordered by voltage from lower to higher.

In Example 64, the subject matter of Example 63 includes, wherein the voltage distribution position for state three is moved downward.

In Example 65, the subject matter of Examples 63-64 includes, wherein the voltage distribution position for seven is moved downward.

In Example 66, the subject matter of Examples 63-65 includes, wherein the voltage distribution position for state four is moved upward.

In Example 67, the subject matter of Examples 54-66 includes, wherein the unmodified encoding has four discrete states.

In Example 68, the subject matter of Example 67 includes, wherein the modified encoding has two discrete states.

In Example 69, the subject matter of Examples 54-68 includes, means for performing a read operation on the NAND cell using the unmodified encoding.

In Example 70, the subject matter of Examples 54-69 includes, means for obtaining a clearance of the high-temperature indicator; means for performing maintenance on the NAND cell to free the NAND cell for another write operation; means for receiving a second write operation; and means for performing the second write operation on the NAND cell using the unmodified encoding in response to clearance of the high-temperature indicator.

Example 71 is at least one machine-readable medium including instructions that, when executed by processing circuitry, cause the processing circuitry to perform operations to implement of any of Examples 1-70.

Example 72 is an apparatus comprising means to implement of any of Examples 1-70.

Example 73 is a system to implement of any of Examples 1-70.

Example 74 is a method to implement of any of Examples 1-70.

The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to herein as “examples”. Such examples can include elements in addition to those shown or described. However, the present inventors also contemplate examples in which only those elements shown or described are provided. Moreover, the present inventors also contemplate examples using any combination or permutation of those elements shown or described (or one or more aspects thereof), either with respect to a particular example (or one or more aspects thereof), or with respect to other examples (or one or more aspects thereof) shown or described herein.

In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of “at least one” or “one or more.” In this document, the term “or” is used to refer to a nonexclusive or, such that “A or B” may include “A but not B,” “B but not A,” and “A and B,” unless otherwise indicated. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein”. Also, in the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

In various examples, the components, controllers, processors, units, engines, or tables described herein can include, among other things, physical circuitry or firmware stored on a physical device. As used herein, “processor” means any type of computational circuit such as, but not limited to, a microprocessor, a microcontroller, a graphics processor, a digital signal processor (DSP), or any other type of processor or processing circuit, including a group of processors or multi-core devices.

The term “horizontal” as used in this document is defined as a plane parallel to the conventional plane or surface of a substrate, such as that underlying a wafer or die, regardless of the actual orientation of the substrate at any point in time. The term “vertical” refers to a direction perpendicular to the horizontal as defined above. Prepositions, such as “on,” “over,” and “under” are defined with respect to the conventional plane or surface being on the top or exposed surface of the substrate, regardless of the orientation of the substrate; and while “on” is intended to suggest a direct contact of one structure relative to another structure which it lies “on” (in the absence of an express indication to the contrary); the terms “over” and “under” are expressly intended to identify a relative placement of structures (or layers, features, etc.), which expressly includes—but is not limited to—direct contact between the identified structures unless specifically identified as such. Similarly, the terms “over” and “under” are not limited to horizontal orientations, as a structure may be “over” a referenced structure if it is, at some point in time, an outermost portion of the construction under discussion, even if such structure extends vertically relative to the referenced structure, rather than in a horizontal orientation.

The terms “wafer” and “substrate” are used herein to refer generally to any structure on which integrated circuits are formed, and also to such structures during various stages of integrated circuit fabrication. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the various embodiments is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.

Various embodiments according to the present disclosure and described herein include memory utilizing a vertical structure of memory cells (e.g., NAND strings of memory cells). As used herein, directional adjectives will be taken relative a surface of a substrate upon which the memory cells are formed (i.e., a vertical structure will be taken as extending away from the substrate surface, a bottom end of the vertical structure will be taken as the end nearest the substrate surface and a top end of the vertical structure will be taken as the end farthest from the substrate surface).

As used herein, directional adjectives, such as horizontal, vertical, normal, parallel, perpendicular, etc., can refer to relative orientations, and are not intended to require strict adherence to specific geometric properties, unless otherwise noted. For example, as used herein, a vertical structure need not be strictly perpendicular to a surface of a substrate, but may instead be generally perpendicular to the surface of the substrate, and may form an acute angle with the surface of the substrate (e.g., between 60 and 120 degrees, etc.).

In some embodiments described herein, different doping configurations may be applied to a source-side select gate (SGS), a control gate (CG), and a drain-side select gate (SGD), each of which, in this example, may be formed of or at least include polysilicon, with the result such that these tiers (e.g., polysilicon, etc.) may have different etch rates when exposed to an etching solution. For example, in a process of forming a monolithic pillar in a 3D semiconductor device, the SGS and the CG may form recesses, while the SGD may remain less recessed or even not recessed. These doping configurations may thus enable selective etching into the distinct tiers (e.g., SGS, CG, and SGD) in the 3D semiconductor device by using an etching solution (e.g., tetramethylammonium hydroxide (TMCH)).

Operating a memory cell, as used herein, includes reading from, writing to, or erasing the memory cell. The operation of placing a memory cell in an intended state is referred to herein as “programming,” and can include both writing to or erasing from the memory cell (e.g., the memory cell may be programmed to an erased state).

According to one or more embodiments of the present disclosure, a memory controller (e.g., a processor, controller, firmware, etc.) located internal or external to a memory device, is capable of determining (e.g., selecting, setting, adjusting, computing, changing, clearing, communicating, adapting, deriving, defining, utilizing, modifying, applying, etc.) a quantity of wear cycles, or a wear state (e.g., recording wear cycles, counting operations of the memory device as they occur, tracking the operations of the memory device it initiates, evaluating the memory device characteristics corresponding to a wear state, etc.)

According to one or more embodiments of the present disclosure, a memory access device may be configured to provide wear cycle information to the memory device with each memory operation. The memory device control circuitry (e.g., control logic) may be programmed to compensate for memory device performance changes corresponding to the wear cycle information. The memory device may receive the wear cycle information and determine one or more operating parameters (e.g., a value, characteristic) in response to the wear cycle information.

It will be understood that when an element is referred to as being “on,” “connected to” or “coupled with” another element, it can be directly on, connected, or coupled with the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled with” another element, there are no intervening elements or layers present. If two elements are shown in the drawings with a line connecting them, the two elements can be either be coupled, or directly coupled, unless otherwise indicated.

Method examples described herein can be machine or computer-implemented at least in part. Some examples can include a computer-readable medium or machine-readable medium encoded with instructions operable to configure an electronic device to perform methods as described in the above examples. An implementation of such methods can include code, such as microcode, assembly language code, a higher-level language code, or the like. Such code can include computer readable instructions for performing various methods. The code may form portions of computer program products. Further, the code can be tangibly stored on one or more volatile or non-volatile tangible computer-readable media, such as during execution or at other times. Examples of these tangible computer-readable media can include, but are not limited to, hard disks, removable magnetic disks, removable optical disks (e.g., compact discs and digital video disks), magnetic cassettes, memory cards or sticks, random access memories (RAMs), read only memories (ROMs), solid state drives (SSDs), Universal Flash Storage (UFS) device, embedded MMC (eMMC) device, and the like.

The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment, and it is contemplated that such embodiments can be combined with each other in various combinations or permutations. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. 

The invention claimed is:
 1. A non-transitory machine-readable medium including instructions for temperature-sensitive cell encoding, the instructions, when executed by circuitry on a device to program a NAND cell, cause the circuitry to perform operations comprising: obtaining a temperature; selecting a NAND cell encoding from a base encoding based on the temperature; and programming the NAND cell with the encoding, wherein the selected encoding differs from the base encoding by using fewer than all voltage distributions that correspond to the base encoding.
 2. The machine-readable medium of claim 1, wherein the NAND cell is read using the base encoding.
 3. The machine-readable medium of claim 1, wherein the voltage distributions used in the selected encoding increase a read margin between two symbols compared to that of the base encoding.
 4. The machine-readable medium of claim 1, wherein the base encoding has eight discrete states, and wherein the selected encoding has four discrete states.
 5. The machine-readable medium of claim 1, wherein multiple programming passes are used to program the NAND cell, and wherein the first pass operates in accordance with a first programming pass of the base encoding, one or more subsequent programming passes enacting the selected encoding.
 6. The machine-readable medium of claim 4, wherein the four discrete states correspond to states zero, three, four, and seven from the eight discrete states, the states ordered by voltage from lower to higher.
 7. The machine-readable medium of claim 6, wherein: the voltage distribution position for state zero is unchanged; the voltage distribution position for state three is moved downward; the voltage distribution position for seven is moved downward; and the voltage distribution position for state four is moved upward.
 8. The machine-readable medium of claim 1, wherein the unmodified encoding has four discrete states, and wherein the modified encoding has two discrete states.
 9. A device for NAND cell encoding, the NAND device comprising: a NAND cell; and a controller to: obtain a temperature; select a NAND cell encoding from a base encoding based on the temperature; and program the NAND cell with the encoding, wherein the selected encoding differs from the base encoding by using fewer than all voltage distributions that correspond to the base encoding.
 10. The device of claim 9, wherein the NAND cell is read using the base encoding.
 11. The device of claim 9, wherein the voltage distributions used in the selected encoding increase a read margin between two symbols compared to that of the base encoding.
 12. The device of claim 9, wherein the base encoding has eight discrete states, and wherein the selected encoding has four discrete states.
 13. The device of claim 9, wherein multiple programming passes are used to program the NAND cell, and wherein the first pass operates in accordance with a first programming pass of the base encoding, one or more subsequent programming passes enacting the selected encoding.
 14. The device of claim 12, wherein the four discrete states correspond to states zero, three, four, and seven from the eight discrete states, the states ordered by voltage from lower to higher.
 15. The device of claim 14, wherein: the voltage distribution position for state zero is unchanged; the voltage distribution position for state three is moved downward; the voltage distribution position for seven is moved downward; and the voltage distribution position for state four is moved upward.
 16. The device of claim 9, wherein the unmodified encoding has four discrete states, and wherein the modified encoding has two discrete states.
 17. A method for temperature-sensitive cell encoding, the method performed by device to program a NAND cell, the method comprising: obtaining a temperature; selecting a NAND cell encoding from a base encoding based on the temperature; and programming the NAND cell with the encoding, wherein the selected encoding differs from the base encoding by using fewer than all voltage distributions that correspond to the base encoding.
 18. The method of claim 17, wherein the NAND cell is read using the base encoding.
 19. The method of claim 17, wherein the voltage distributions used in the selected encoding increase a read margin between two symbols compared to that of the base encoding.
 20. The method of claim 17, wherein the base encoding has eight discrete states, and wherein the selected encoding has four discrete states.
 21. The method of claim 17, wherein multiple programming passes are used to program the NAND cell, and wherein the first pass operates in accordance with a first programming pass of the base encoding, one or more subsequent programming passes enacting the selected encoding.
 22. The method of claim 20, wherein the four discrete states correspond to states zero, three, four, and seven from the eight discrete states, the states ordered by voltage from lower to higher.
 23. The method of claim 22, wherein: the voltage distribution position for state zero is unchanged; the voltage distribution position for state three is moved downward; the voltage distribution position for seven is moved downward; and the voltage distribution position for state four is moved upward.
 24. The method of claim 17, wherein the unmodified encoding has four discrete states, and wherein the modified encoding has two discrete states. 